/*
 * twemproxy - A fast and lightweight proxy for memcached protocol.
 * Copyright (C) 2011 Twitter, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * Copyright (c) 1991, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *    @(#)queue.h    8.5 (Berkeley) 8/20/94
 * $FreeBSD: src/sys/sys/queue.h,v 1.73 2010/02/20 01:05:30 emaste Exp $
 */

#ifndef _NC_QUEUE_H_
#define _NC_QUEUE_H_

#include <nc_log.h>

#ifndef __offsetof
#define __offsetof(type, field) ((size_t)(&((type *)NULL)->field))
#endif

/*
 * This file defines five types of data structures: singly-linked lists,
 * singly-linked tail queues, lists, tail queues, and circular queues.
 *
 * A singly-linked list is headed by a single forward pointer. The elements
 * are singly linked for minimum space and pointer manipulation overhead at
 * the expense of O(n) removal for arbitrary elements. New elements can be
 * added to the list after an existing element or at the head of the list.
 * Elements being removed from the head of the list should use the explicit
 * macro for this purpose for optimum efficiency. A singly-linked list may
 * only be traversed in the forward direction.  Singly-linked lists are ideal
 * for applications with large datasets and few or no removals or for
 * implementing a LIFO queue.
 *
 * A singly-linked tail queue is headed by a pair of pointers, one to the
 * head of the list and the other to the tail of the list. The elements are
 * singly linked for minimum space and pointer manipulation overhead at the
 * expense of O(n) removal for arbitrary elements. New elements can be added
 * to the list after an existing element, at the head of the list, or at the
 * end of the list. Elements being removed from the head of the tail queue
 * should use the explicit macro for this purpose for optimum efficiency.
 * A singly-linked tail queue may only be traversed in the forward direction.
 * Singly-linked tail queues are ideal for applications with large datasets
 * and few or no removals or for implementing a FIFO queue.
 *
 * A list is headed by a single forward pointer (or an array of forward
 * pointers for a hash table header). The elements are doubly linked
 * so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before
 * or after an existing element or at the head of the list. A list
 * may only be traversed in the forward direction.
 *
 * A tail queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or
 * after an existing element, at the head of the list, or at the end of
 * the list. A tail queue may be traversed in either direction.
 *
 * A circle queue is headed by a pair of pointers, one to the head of the
 * list and the other to the tail of the list. The elements are doubly
 * linked so that an arbitrary element can be removed without a need to
 * traverse the list. New elements can be added to the list before or after
 * an existing element, at the head of the list, or at the end of the list.
 * A circle queue may be traversed in either direction, but has a more
 * complex end of list detection.
 *
 * For details on the use of these macros, see the queue(3) manual page.
 *
 *
 *                      SLIST   LIST    STAILQ  TAILQ   CIRCLEQ
 * _HEAD                +       +       +       +       +
 * _HEAD_INITIALIZER    +       +       +       +       +
 * _ENTRY               +       +       +       +       +
 * _INIT                +       +       +       +       +
 * _EMPTY               +       +       +       +       +
 * _FIRST               +       +       +       +       +
 * _NEXT                +       +       +       +       +
 * _PREV                -       -       -       +       +
 * _LAST                -       -       +       +       +
 * _FOREACH             +       +       +       +       +
 * _FOREACH_REVERSE     -       -       -       +       +
 * _INSERT_HEAD         +       +       +       +       +
 * _INSERT_BEFORE       -       +       -       +       +
 * _INSERT_AFTER        +       +       +       +       +
 * _INSERT_TAIL         -       -       +       +       +
 * _REMOVE_HEAD         +       -       +       -       -
 * _REMOVE              +       +       +       +       +
 *
 */

#define QUEUE_MACRO_SCRUB 1

#ifdef NC_ASSERT_PANIC
# define QUEUE_MACRO_TRACE  1
# define QUEUE_MACRO_ASSERT 1
#endif

#ifdef QUEUE_MACRO_SCRUB

#define QMD_SAVELINK(name, link)    void **name = (void *)&(link)

#define TRASHIT(x) do {                                                 \
    (x) = (void *) NULL;                                                \
} while (0)

#else

#define QMD_SAVELINK(name, link)
#define TRASHIT(x)

#endif /* QUEUE_MACRO_SCRUB */

#ifdef QUEUE_MACRO_TRACE

/* Store the last 2 places the queue element or head was altered */
struct qm_trace {
    char *lastfile;
    int  lastline;
    char *prevfile;
    int  prevline;
};

#define TRACEBUF    struct qm_trace trace;

#define QMD_TRACE_HEAD(head) do {                                       \
    (head)->trace.prevline = (head)->trace.lastline;                    \
    (head)->trace.prevfile = (head)->trace.lastfile;                    \
    (head)->trace.lastline = __LINE__;                                  \
    (head)->trace.lastfile = __FILE__;                                  \
} while (0)

#define QMD_TRACE_HEAD_INIT(head) do {                                  \
    (head)->trace.prevline = __LINE__;                                  \
    (head)->trace.prevfile = __FILE__;                                  \
    (head)->trace.lastline = __LINE__;                                  \
    (head)->trace.lastfile = __FILE__;                                  \
} while (0)

#define QMD_TRACE_ELEM(elem) do {                                       \
    (elem)->trace.prevline = (elem)->trace.lastline;                    \
    (elem)->trace.prevfile = (elem)->trace.lastfile;                    \
    (elem)->trace.lastline = __LINE__;                                  \
    (elem)->trace.lastfile = __FILE__;                                  \
} while (0)

#else

#define QMD_TRACE_ELEM(elem)
#define QMD_TRACE_HEAD(head)
#define QMD_TRACE_HEAD_INIT(head)
#define TRACEBUF

#endif /* QUEUE_MACRO_TRACE */

/*
 * Singly-linked List declarations.
 */
#define SLIST_HEAD(name, type)                                          \
struct name {                                                           \
    struct type *slh_first; /* first element */                         \
}

#define SLIST_HEAD_INITIALIZER(head)                                    \
    { NULL }

#define SLIST_ENTRY(type)                                               \
struct {                                                                \
    struct type *sle_next;  /* next element */                          \
}

/*
 * Singly-linked List functions.
 */
#define SLIST_EMPTY(head)    ((head)->slh_first == NULL)

#define SLIST_FIRST(head)    ((head)->slh_first)

#define SLIST_FOREACH(var, head, field)                                 \
    for ((var) = SLIST_FIRST((head));                                   \
        (var);                                                          \
        (var) = SLIST_NEXT((var), field))

#define SLIST_FOREACH_SAFE(var, head, field, tvar)                      \
    for ((var) = SLIST_FIRST((head));                                   \
        (var) && ((tvar) = SLIST_NEXT((var), field), 1);                \
        (var) = (tvar))

#define SLIST_FOREACH_PREVPTR(var, varp, head, field)                   \
    for ((varp) = &SLIST_FIRST((head));                                 \
        ((var) = *(varp)) != NULL;                                      \
        (varp) = &SLIST_NEXT((var), field))

#define SLIST_INIT(head) do {                                           \
    SLIST_FIRST((head)) = NULL;                                         \
} while (0)

#define SLIST_INSERT_AFTER(slistelm, elm, field) do {                   \
    SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);           \
    SLIST_NEXT((slistelm), field) = (elm);                              \
} while (0)

#define SLIST_INSERT_HEAD(head, elm, field) do {                        \
    SLIST_NEXT((elm), field) = SLIST_FIRST((head));                     \
    SLIST_FIRST((head)) = (elm);                                        \
} while (0)

#define SLIST_NEXT(elm, field)    ((elm)->field.sle_next)

#define SLIST_REMOVE(head, elm, type, field) do {                       \
    if (SLIST_FIRST((head)) == (elm)) {                                 \
        SLIST_REMOVE_HEAD((head), field);                               \
    } else {                                                            \
        struct type *curelm = SLIST_FIRST((head));                      \
        while (SLIST_NEXT(curelm, field) != (elm)) {                    \
            curelm = SLIST_NEXT(curelm, field);                         \
        }                                                               \
        SLIST_REMOVE_AFTER(curelm, field);                              \
    }                                                                   \
} while (0)

#define SLIST_REMOVE_AFTER(elm, field) do {                             \
    QMD_SAVELINK(oldnext, SLIST_NEXT(SLIST_NEXT(elm, field), field));   \
    SLIST_NEXT(elm, field) = SLIST_NEXT(SLIST_NEXT(elm, field), field); \
    TRASHIT(*oldnext);                                                  \
} while (0)

#define SLIST_REMOVE_HEAD(head, field) do {                             \
    QMD_SAVELINK(oldnext, SLIST_NEXT(SLIST_FIRST((head)), field));      \
    SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);       \
    TRASHIT(*oldnext);                                                  \
} while (0)

/*
 * Singly-linked Tail queue declarations.
 */
#define STAILQ_HEAD(name, type)                                         \
struct name {                                                           \
    struct type *stqh_first; /* first element */                        \
    struct type **stqh_last; /* addr of last next element */            \
}

#define STAILQ_HEAD_INITIALIZER(head)                                   \
    { NULL, &(head).stqh_first }

#define STAILQ_ENTRY(type)                                              \
struct {                                                                \
    struct type *stqe_next;    /* next element */                       \
}

/*
 * Singly-linked Tail queue functions.
 */
#define STAILQ_CONCAT(head1, head2) do {                                \
    if (!STAILQ_EMPTY((head2))) {                                       \
        *(head1)->stqh_last = (head2)->stqh_first;                      \
        (head1)->stqh_last = (head2)->stqh_last;                        \
        STAILQ_INIT((head2));                                           \
    }                                                                   \
} while (0)

#define STAILQ_EMPTY(head)    ((head)->stqh_first == NULL)

#define STAILQ_FIRST(head)    ((head)->stqh_first)

#define STAILQ_FOREACH(var, head, field)                                \
    for ((var) = STAILQ_FIRST((head));                                  \
         (var);                                                         \
         (var) = STAILQ_NEXT((var), field))

#define STAILQ_FOREACH_SAFE(var, head, field, tvar)                     \
    for ((var) = STAILQ_FIRST((head));                                  \
        (var) && ((tvar) = STAILQ_NEXT((var), field), 1);               \
        (var) = (tvar))

#define STAILQ_INIT(head) do {                                          \
    STAILQ_FIRST((head)) = NULL;                                        \
    (head)->stqh_last = &STAILQ_FIRST((head));                          \
} while (0)

#define STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {               \
    if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
        (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
    STAILQ_NEXT((tqelm), field) = (elm);                                \
} while (0)

#define STAILQ_INSERT_HEAD(head, elm, field) do {                       \
    if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL)     \
        (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
    STAILQ_FIRST((head)) = (elm);                                       \
} while (0)

#define STAILQ_INSERT_TAIL(head, elm, field) do {                       \
    STAILQ_NEXT((elm), field) = NULL;                                   \
    *(head)->stqh_last = (elm);                                         \
    (head)->stqh_last = &STAILQ_NEXT((elm), field);                     \
} while (0)

#define STAILQ_LAST(head, type, field)                                  \
    (STAILQ_EMPTY((head)) ?                                             \
        NULL :                                                          \
            ((struct type *)(void *)                                    \
        ((char *)((head)->stqh_last) - __offsetof(struct type, field))))

#define STAILQ_NEXT(elm, field)    ((elm)->field.stqe_next)

#define STAILQ_REMOVE(head, elm, type, field) do {                      \
    if (STAILQ_FIRST((head)) == (elm)) {                                \
        STAILQ_REMOVE_HEAD((head), field);                              \
    }                                                                   \
    else {                                                              \
        struct type *curelm = STAILQ_FIRST((head));                     \
        while (STAILQ_NEXT(curelm, field) != (elm))                     \
            curelm = STAILQ_NEXT(curelm, field);                        \
        STAILQ_REMOVE_AFTER(head, curelm, field);                       \
    }                                                                   \
} while (0)

#define STAILQ_REMOVE_HEAD(head, field) do {                            \
    QMD_SAVELINK(oldnext, STAILQ_NEXT(STAILQ_FIRST((head)), field));    \
    if ((STAILQ_FIRST((head)) =                                         \
         STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL) {           \
        (head)->stqh_last = &STAILQ_FIRST((head));                      \
    }                                                                   \
    TRASHIT(*oldnext);                                                  \
} while (0)

#define STAILQ_REMOVE_AFTER(head, elm, field) do {                      \
    QMD_SAVELINK(oldnext, STAILQ_NEXT(STAILQ_NEXT(elm, field), field)); \
    if ((STAILQ_NEXT(elm, field) =                                      \
         STAILQ_NEXT(STAILQ_NEXT(elm, field), field)) == NULL) {        \
        (head)->stqh_last = &STAILQ_NEXT((elm), field);                 \
    }                                                                   \
    TRASHIT(*oldnext);                                                  \
} while (0)

#define STAILQ_SWAP(head1, head2, type) do {                            \
    struct type *swap_first = STAILQ_FIRST(head1);                      \
    struct type **swap_last = (head1)->stqh_last;                       \
    STAILQ_FIRST(head1) = STAILQ_FIRST(head2);                          \
    (head1)->stqh_last = (head2)->stqh_last;                            \
    STAILQ_FIRST(head2) = swap_first;                                   \
    (head2)->stqh_last = swap_last;                                     \
    if (STAILQ_EMPTY(head1))                                            \
        (head1)->stqh_last = &STAILQ_FIRST(head1);                      \
    if (STAILQ_EMPTY(head2))                                            \
        (head2)->stqh_last = &STAILQ_FIRST(head2);                      \
} while (0)


/*
 * List declarations.
 */
#define LIST_HEAD(name, type)                                           \
struct name {                                                           \
    struct type *lh_first; /* first element */                          \
}

#define LIST_HEAD_INITIALIZER(head)                                     \
    { NULL }

#define LIST_ENTRY(type)                                                \
struct {                                                                \
    struct type *le_next;  /* next element */                           \
    struct type **le_prev; /* address of previous next element */       \
}

/*
 * List functions.
 */

#ifdef QUEUE_MACRO_ASSERT

#define QMD_LIST_CHECK_HEAD(head, field) do {                               \
    if (LIST_FIRST((head)) != NULL &&                                       \
        LIST_FIRST((head))->field.le_prev != &LIST_FIRST((head))) {         \
        log_panic("Bad list head %p first->prev != head", (void *)(head));  \
    }                                                                       \
} while (0)

#define QMD_LIST_CHECK_NEXT(elm, field) do {                                \
    if (LIST_NEXT((elm), field) != NULL &&                                  \
        LIST_NEXT((elm), field)->field.le_prev != &((elm)->field.le_next)) {\
        log_panic("Bad link elm %p next->prev != elm",(void *)(elm));       \
    }                                                                       \
} while (0)

#define QMD_LIST_CHECK_PREV(elm, field) do {                            \
    if (*(elm)->field.le_prev != (elm)) {                               \
        log_panic("Bad link elm %p prev->next != elm",(void *)(elm));   \
    }                                                                   \
} while (0)

#else

#define QMD_LIST_CHECK_HEAD(head, field)
#define QMD_LIST_CHECK_NEXT(elm, field)
#define QMD_LIST_CHECK_PREV(elm, field)

#endif /* QUEUE_MACRO_ASSERT */

#define LIST_EMPTY(head)    ((head)->lh_first == NULL)

#define LIST_FIRST(head)    ((head)->lh_first)

#define LIST_FOREACH(var, head, field)                                  \
    for ((var) = LIST_FIRST((head));                                    \
        (var);                                                          \
        (var) = LIST_NEXT((var), field))

#define LIST_FOREACH_SAFE(var, head, field, tvar)                       \
    for ((var) = LIST_FIRST((head));                                    \
        (var) && ((tvar) = LIST_NEXT((var), field), 1);                 \
        (var) = (tvar))

#define LIST_INIT(head) do {                                            \
    LIST_FIRST((head)) = NULL;                                          \
} while (0)

#define LIST_INSERT_AFTER(listelm, elm, field) do {                     \
    QMD_LIST_CHECK_NEXT(listelm, field);                                \
    if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
        LIST_NEXT((listelm), field)->field.le_prev =                    \
            &LIST_NEXT((elm), field);                                   \
    LIST_NEXT((listelm), field) = (elm);                                \
    (elm)->field.le_prev = &LIST_NEXT((listelm), field);                \
} while (0)

#define LIST_INSERT_BEFORE(listelm, elm, field) do {                    \
    QMD_LIST_CHECK_PREV(listelm, field);                                \
    (elm)->field.le_prev = (listelm)->field.le_prev;                    \
    LIST_NEXT((elm), field) = (listelm);                                \
    *(listelm)->field.le_prev = (elm);                                  \
    (listelm)->field.le_prev = &LIST_NEXT((elm), field);                \
} while (0)

#define LIST_INSERT_HEAD(head, elm, field) do {                         \
    QMD_LIST_CHECK_HEAD((head), field);                                 \
    if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)         \
        LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);   \
    LIST_FIRST((head)) = (elm);                                         \
    (elm)->field.le_prev = &LIST_FIRST((head));                         \
} while (0)

#define LIST_NEXT(elm, field)    ((elm)->field.le_next)

#define LIST_REMOVE(elm, field) do {                                    \
    QMD_SAVELINK(oldnext, (elm)->field.le_next);                        \
    QMD_SAVELINK(oldprev, (elm)->field.le_prev);                        \
    QMD_LIST_CHECK_NEXT(elm, field);                                    \
    QMD_LIST_CHECK_PREV(elm, field);                                    \
    if (LIST_NEXT((elm), field) != NULL)                                \
        LIST_NEXT((elm), field)->field.le_prev =                        \
            (elm)->field.le_prev;                                       \
    *(elm)->field.le_prev = LIST_NEXT((elm), field);                    \
    TRASHIT(*oldnext);                                                  \
    TRASHIT(*oldprev);                                                  \
} while (0)

#define LIST_SWAP(head1, head2, type, field) do {                       \
    struct type *swap_tmp = LIST_FIRST((head1));                        \
    LIST_FIRST((head1)) = LIST_FIRST((head2));                          \
    LIST_FIRST((head2)) = swap_tmp;                                     \
    if ((swap_tmp = LIST_FIRST((head1))) != NULL)                       \
        swap_tmp->field.le_prev = &LIST_FIRST((head1));                 \
    if ((swap_tmp = LIST_FIRST((head2))) != NULL)                       \
        swap_tmp->field.le_prev = &LIST_FIRST((head2));                 \
} while (0)

/*
 * Tail queue declarations.
 */
#define TAILQ_HEAD(name, type)                                          \
struct name {                                                           \
    struct type *tqh_first; /* first element */                         \
    struct type **tqh_last; /* addr of last next element */             \
    TRACEBUF                                                            \
}

#define TAILQ_HEAD_INITIALIZER(head)                                    \
    { NULL, &(head).tqh_first }

#define TAILQ_ENTRY(type)                                               \
struct {                                                                \
    struct type *tqe_next;  /* next element */                          \
    struct type **tqe_prev; /* address of previous next element */      \
    TRACEBUF                                                            \
}

/*
 * Tail queue functions.
 */
#ifdef QUEUE_MACRO_ASSERT

#define QMD_TAILQ_CHECK_HEAD(head, field) do {                              \
    if (!TAILQ_EMPTY(head) &&                                               \
        TAILQ_FIRST((head))->field.tqe_prev != &TAILQ_FIRST((head))) {      \
        log_panic("Bad tailq head %p first->prev != head", (void *)(head)); \
    }                                                                       \
} while (0)

#define QMD_TAILQ_CHECK_TAIL(head, field) do {                              \
    if (*(head)->tqh_last != NULL) {                                        \
        log_panic("Bad tailq NEXT(%p->tqh_last) != NULL",(void *)(head));   \
    }                                                                       \
} while (0)

#define QMD_TAILQ_CHECK_NEXT(elm, field) do {                               \
    if (TAILQ_NEXT((elm), field) != NULL &&                                 \
        TAILQ_NEXT((elm), field)->field.tqe_prev != &((elm)->field.tqe_next)) {\
        log_panic("Bad link elm %p next->prev != elm",(void *)(elm));       \
    }                                                                       \
} while (0)

#define QMD_TAILQ_CHECK_PREV(elm, field) do {                           \
    if (*(elm)->field.tqe_prev != (elm)) {                              \
        log_panic("Bad link elm %p prev->next != elm",(void *)(elm));   \
    }                                                                   \
} while (0)

#else

#define QMD_TAILQ_CHECK_HEAD(head, field)
#define QMD_TAILQ_CHECK_TAIL(head, headname)
#define QMD_TAILQ_CHECK_NEXT(elm, field)
#define QMD_TAILQ_CHECK_PREV(elm, field)

#endif /* QUEUE_MACRO_ASSERT */

#define TAILQ_CONCAT(head1, head2, field) do {                          \
    if (!TAILQ_EMPTY(head2)) {                                          \
        *(head1)->tqh_last = (head2)->tqh_first;                        \
        (head2)->tqh_first->field.tqe_prev = (head1)->tqh_last;         \
        (head1)->tqh_last = (head2)->tqh_last;                          \
        TAILQ_INIT((head2));                                            \
        QMD_TRACE_HEAD(head1);                                          \
        QMD_TRACE_HEAD(head2);                                          \
    }                                                                   \
} while (0)

#define TAILQ_EMPTY(head)    ((head)->tqh_first == NULL)

#define TAILQ_FIRST(head)    ((head)->tqh_first)

#define TAILQ_FOREACH(var, head, field)                                 \
    for ((var) = TAILQ_FIRST((head));                                   \
        (var);                                                          \
        (var) = TAILQ_NEXT((var), field))

#define TAILQ_FOREACH_SAFE(var, head, field, tvar)                      \
    for ((var) = TAILQ_FIRST((head));                                   \
        (var) && ((tvar) = TAILQ_NEXT((var), field), 1);                \
        (var) = (tvar))

#define TAILQ_FOREACH_REVERSE(var, head, headname, field)               \
    for ((var) = TAILQ_LAST((head), headname);                          \
        (var);                                                          \
        (var) = TAILQ_PREV((var), headname, field))

#define TAILQ_FOREACH_REVERSE_SAFE(var, head, headname, field, tvar)    \
    for ((var) = TAILQ_LAST((head), headname);                          \
        (var) && ((tvar) = TAILQ_PREV((var), headname, field), 1);      \
        (var) = (tvar))

#define TAILQ_INIT(head) do {                                           \
    TAILQ_FIRST((head)) = NULL;                                         \
    (head)->tqh_last = &TAILQ_FIRST((head));                            \
    QMD_TRACE_HEAD_INIT(head);                                               \
} while (0)

#define TAILQ_INSERT_AFTER(head, listelm, elm, field) do {              \
    QMD_TAILQ_CHECK_NEXT(listelm, field);                               \
    if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL) {  \
        TAILQ_NEXT((elm), field)->field.tqe_prev =  &TAILQ_NEXT((elm), field);\
    } else {                                                            \
        (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
        QMD_TRACE_HEAD(head);                                           \
    }                                                                   \
    TAILQ_NEXT((listelm), field) = (elm);                               \
    (elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);              \
    QMD_TRACE_ELEM(&(elm)->field);                                      \
    QMD_TRACE_ELEM(&listelm->field);                                    \
} while (0)

#define TAILQ_INSERT_BEFORE(listelm, elm, field) do {                   \
    QMD_TAILQ_CHECK_PREV(listelm, field);                               \
    (elm)->field.tqe_prev = (listelm)->field.tqe_prev;                  \
    TAILQ_NEXT((elm), field) = (listelm);                               \
    *(listelm)->field.tqe_prev = (elm);                                 \
    (listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);              \
    QMD_TRACE_ELEM(&(elm)->field);                                      \
    QMD_TRACE_ELEM(&listelm->field);                                    \
} while (0)

#define TAILQ_INSERT_HEAD(head, elm, field) do {                        \
    QMD_TAILQ_CHECK_HEAD(head, field);                                  \
    if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)       \
        TAILQ_FIRST((head))->field.tqe_prev =                           \
            &TAILQ_NEXT((elm), field);                                  \
    else                                                                \
        (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
    TAILQ_FIRST((head)) = (elm);                                        \
    (elm)->field.tqe_prev = &TAILQ_FIRST((head));                       \
    QMD_TRACE_HEAD(head);                                               \
    QMD_TRACE_ELEM(&(elm)->field);                                      \
} while (0)

#define TAILQ_INSERT_TAIL(head, elm, field) do {                        \
    QMD_TAILQ_CHECK_TAIL(head, field);                                  \
    TAILQ_NEXT((elm), field) = NULL;                                    \
    (elm)->field.tqe_prev = (head)->tqh_last;                           \
    *(head)->tqh_last = (elm);                                          \
    (head)->tqh_last = &TAILQ_NEXT((elm), field);                       \
    QMD_TRACE_HEAD(head);                                               \
    QMD_TRACE_ELEM(&(elm)->field);                                      \
} while (0)

#define TAILQ_LAST(head, headname)                                      \
    (*(((struct headname *)((head)->tqh_last))->tqh_last))

#define TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)

#define TAILQ_PREV(elm, headname, field)                                \
    (*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))

#define TAILQ_REMOVE(head, elm, field) do {                             \
    QMD_SAVELINK(oldnext, (elm)->field.tqe_next);                       \
    QMD_SAVELINK(oldprev, (elm)->field.tqe_prev);                       \
    QMD_TAILQ_CHECK_NEXT(elm, field);                                   \
    QMD_TAILQ_CHECK_PREV(elm, field);                                   \
    if ((TAILQ_NEXT((elm), field)) != NULL) {                           \
        TAILQ_NEXT((elm), field)->field.tqe_prev =                      \
            (elm)->field.tqe_prev;                                      \
    } else {                                                            \
        (head)->tqh_last = (elm)->field.tqe_prev;                       \
        QMD_TRACE_HEAD(head);                                           \
    }                                                                   \
    *(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);                  \
    TRASHIT(*oldnext);                                                  \
    TRASHIT(*oldprev);                                                  \
    QMD_TRACE_ELEM(&(elm)->field);                                      \
} while (0)

#define TAILQ_SWAP(head1, head2, type, field) do {                      \
    struct type *swap_first = (head1)->tqh_first;                       \
    struct type **swap_last = (head1)->tqh_last;                        \
    (head1)->tqh_first = (head2)->tqh_first;                            \
    (head1)->tqh_last = (head2)->tqh_last;                              \
    (head2)->tqh_first = swap_first;                                    \
    (head2)->tqh_last = swap_last;                                      \
    if ((swap_first = (head1)->tqh_first) != NULL)                      \
        swap_first->field.tqe_prev = &(head1)->tqh_first;               \
    else                                                                \
        (head1)->tqh_last = &(head1)->tqh_first;                        \
    if ((swap_first = (head2)->tqh_first) != NULL)                      \
        swap_first->field.tqe_prev = &(head2)->tqh_first;               \
    else                                                                \
        (head2)->tqh_last = &(head2)->tqh_first;                        \
} while (0)

/*
 * Circular queue declarations.
 */
#define CIRCLEQ_HEAD(name, type)                                        \
struct name {                                                           \
    struct type *cqh_first; /* first element */                         \
    struct type *cqh_last;  /* last element */                          \
}

#define CIRCLEQ_HEAD_INITIALIZER(head)                                  \
    { (void *)&(head), (void *)&(head) }

#define CIRCLEQ_ENTRY(type)                                             \
struct {                                                                \
    struct type *cqe_next; /* next element */                           \
    struct type *cqe_prev; /* previous element */                       \
}

/*
 * Circular queue functions.
 */
#define CIRCLEQ_EMPTY(head) ((head)->cqh_first == (void *)(head))

#define CIRCLEQ_FIRST(head) ((head)->cqh_first)

#define CIRCLEQ_FOREACH(var, head, field)                               \
    for ((var) = CIRCLEQ_FIRST((head));                                 \
        (var) != (void *)(head) || ((var) = NULL);                      \
        (var) = CIRCLEQ_NEXT((var), field))

#define CIRCLEQ_FOREACH_REVERSE(var, head, field)                       \
    for ((var) = CIRCLEQ_LAST((head));                                  \
        (var) != (void *)(head) || ((var) = NULL);                      \
        (var) = CIRCLEQ_PREV((var), field))

#define CIRCLEQ_INIT(head) do {                                         \
    CIRCLEQ_FIRST((head)) = (void *)(head);                             \
    CIRCLEQ_LAST((head)) = (void *)(head);                              \
} while (0)

#define CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {            \
    CIRCLEQ_NEXT((elm), field) = CIRCLEQ_NEXT((listelm), field);        \
    CIRCLEQ_PREV((elm), field) = (listelm);                             \
    if (CIRCLEQ_NEXT((listelm), field) == (void *)(head))               \
        CIRCLEQ_LAST((head)) = (elm);                                   \
    else                                                                \
        CIRCLEQ_PREV(CIRCLEQ_NEXT((listelm), field), field) = (elm);    \
    CIRCLEQ_NEXT((listelm), field) = (elm);                             \
} while (0)

#define CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {           \
    CIRCLEQ_NEXT((elm), field) = (listelm);                             \
    CIRCLEQ_PREV((elm), field) = CIRCLEQ_PREV((listelm), field);        \
    if (CIRCLEQ_PREV((listelm), field) == (void *)(head))               \
        CIRCLEQ_FIRST((head)) = (elm);                                  \
    else                                                                \
        CIRCLEQ_NEXT(CIRCLEQ_PREV((listelm), field), field) = (elm);    \
    CIRCLEQ_PREV((listelm), field) = (elm);                             \
} while (0)

#define CIRCLEQ_INSERT_HEAD(head, elm, field) do {                      \
    CIRCLEQ_NEXT((elm), field) = CIRCLEQ_FIRST((head));                 \
    CIRCLEQ_PREV((elm), field) = (void *)(head);                        \
    if (CIRCLEQ_LAST((head)) == (void *)(head))                         \
        CIRCLEQ_LAST((head)) = (elm);                                   \
    else                                                                \
        CIRCLEQ_PREV(CIRCLEQ_FIRST((head)), field) = (elm);             \
    CIRCLEQ_FIRST((head)) = (elm);                                      \
} while (0)

#define CIRCLEQ_INSERT_TAIL(head, elm, field) do {                      \
    CIRCLEQ_NEXT((elm), field) = (void *)(head);                        \
    CIRCLEQ_PREV((elm), field) = CIRCLEQ_LAST((head));                  \
    if (CIRCLEQ_FIRST((head)) == (void *)(head))                        \
        CIRCLEQ_FIRST((head)) = (elm);                                  \
    else                                                                \
        CIRCLEQ_NEXT(CIRCLEQ_LAST((head)), field) = (elm);              \
    CIRCLEQ_LAST((head)) = (elm);                                       \
} while (0)

#define CIRCLEQ_LAST(head) ((head)->cqh_last)

#define CIRCLEQ_NEXT(elm,field) ((elm)->field.cqe_next)

#define CIRCLEQ_PREV(elm,field) ((elm)->field.cqe_prev)

#define CIRCLEQ_REMOVE(head, elm, field) do {                           \
    if (CIRCLEQ_NEXT((elm), field) == (void *)(head))                   \
        CIRCLEQ_LAST((head)) = CIRCLEQ_PREV((elm), field);              \
    else                                                                \
        CIRCLEQ_PREV(CIRCLEQ_NEXT((elm), field), field) =               \
            CIRCLEQ_PREV((elm), field);                                 \
    if (CIRCLEQ_PREV((elm), field) == (void *)(head))                   \
        CIRCLEQ_FIRST((head)) = CIRCLEQ_NEXT((elm), field);             \
    else                                                                \
        CIRCLEQ_NEXT(CIRCLEQ_PREV((elm), field), field) =               \
            CIRCLEQ_NEXT((elm), field);                                 \
} while (0)

#endif
